Arm design - rotation mechanism?

[n0cturnalxb]

I was discussing a design I came up with with a mentor on my team and he mentioned that getting a part of the arm (eg the manipulator) the rotate the way I wanted it to would be difficult/complex. Annd.. since I'm no engineer (yet! HA -cough-), I wanted to ask..

Just how complex is it to get a part of your arm to rotate? Preferably 180 degrees..

For example, something like this:

Before rotation:

||==

After rotation:

==||

It'd just be the horizontal part that would be rotating, I guess.

If it's mechanically feasible and not overly complex, how weak would the rotating horizontal part become? Would it be able to sustain a good amount of vertical force without falling apart (breaking) or malfunctioning?

If there is any information related to this outside of ChiefDelphi, please point me there :) I'd greatly appreciate it.

Thanks!


PS: I'd imagine the rotation would have to depend on a motor or something, but I'm not completely sure how difficult/complex it would be to build something that works smoothly/consistently like that.


[edit] SteveO brought up a point I failed to address.. the horizontal bar would be rotating up and over (vertically), not right to left/left to right (horizontally).

[Arefin Bari]

Rotation isn't very hard to do. simple gear reduction or usage of sprocket and chain can let you do rotations easily. Use a turret or lazy susan.

-Arefin.

[SteveO]

That bar you have, is it rotating from left to right or up and over? Rotating it from left to right like Arefin says with a turret is mechanically feasible and pretty easy to set up.
If it's mechanically feasible and not overly complex, how weak would the rotating horizontal part become? Would it be able to sustain a good amount of vertical force without falling apart (breaking) or malfunctioning?You can make an arm pretty beefy depending on what access you have to materials and machines. Usually for us its more difficult to stay under weight than have things tough enough.

[n0cturnalxb]

That bar you have, is it rotating from left to right or up and over?


Oops.. it should be rotating up and over. Editing post now, sorry about that.

[SteveO]

It's definitely feasible, and its what we plan to do as well. Your main obstacle is getting enough torque out of whatever you are using to rotate it. You can do this with gear/pulley reduction and a strong enough motor. We're thinking the Fisher Price...

[n0cturnalxb]

It's definitely feasible, and its what we plan to do as well. Your main obstacle is getting enough torque out of whatever you are using to rotate it. You can do this with gear/pulley reduction and a strong enough motor. We're thinking the Fisher Price...


But would implementing rotation weaken the device? As in.. with rotation, would it still be able to hold as much weight as it could without rotation?

My team's main concern, as far as I know, is complexity.. would it be easy to break but difficult to fix, for example?

Sorry for the incessant questions, and thanks for your quick responses :)

[SteveO]

Well, yes it would weaken it, but then you would only have a solid non-maneuverable bar :D. It shouldn't be too complex to replace if it breaks or malfunctions; we made a bar that rotated like you are describing last year out of modified 2" aluminum square tubing. It was light and durable and really easy to make replacements. Just remember that the arm is going to be most vulnerable at that joint that it rotates, so try to reinforce that as best you can. Also, torquing that arm in a direction perpendicular to its rotation is whats going to be your biggest concern with all these robots crashing into each other and entangling arms (at least thats what our problem was last year).